Solar System Ices and Icy Bodies

Possibilities for Europa's ice shell
Scientists are all but certain that Europa has an ocean underneath its icy surface, but they do not know how thick this ice might be. This artist concept illustrates two possible cut-away views through Europa's ice shell.
 

Ices are found in numerous locations in the universe and play a key role in the chemistry, physics and evolution of bodies within planetary systems. Researchers in this area represent a diverse range of backgrounds and expertise focused on investigating the whole range of ices in the solar system. There is a strong focus on the icy moons of Jupiter and Saturn, such as Europa, Ganymede, Enceladus, Titan, and Triton. Also of interest are comets, Kuiper Belt Objects (KBOs), NEOs and asteroids, and the polar regions of Mars. Research in this field contributes to our understanding the formation and evolution of icy bodies and the Solar System as a whole.

 


Selected Research Efforts

 

Thermophysical, Rheological and Mechanical Measurements of Icy Compositions with Application to Solar System Ices

The purpose of this research project is to experimentally determine the thermophysical, rheological, and mechanical properties of icy materials (ices and candidate cryolavas) over cryogenic temperatures (between 80 K and 300 K), which are applicable to outer Solar System objects such as the satellites of Jupiter and Saturn, as well as the Martian polar caps and terrestrial ice sheets. The thermophysical, dynamical, and geological evolution of these satellites were modelled using these material properties in support of the following science objectives: (1) to model the geophysical response of icy satellites to tidal excitation; and (2) to model the geological processes of icy satellites. The research strives to understand the evolutionary history of planetary ices, in terms of the geophysical and geologic processes that have occurred in icy worlds around the solar system.

 

Physical Chemistry of Planetary Ices

Infrared spectra of water-ice film
Infrared spectra of unirradiated (blue) and irradiated (red) water-ice film containing isobutane. Note production of alcohols and CO2.
 

The outer Solar System is populated by ice-rich bodies: comets, Kuiper Belt Objects, centaurs, primitive asteroids, and icy planetary satellites. The research objective of the ‘Physical Chemistry of Planetary Ices’ project is to study and develop an understanding of the physical chemistry of ices of the outer Solar System.

The bulk surface icy composition of the satellites of the outer planets is predominantly water ice, with small amounts of co-condensed simple molecules such as NH3, CO2, CO, N2 and CH4, depending upon their condensation distance from the Sun in the primordial solar nebula. The outer surfaces of these satellites respond to particle and photon bombardment from the Sun, the solar wind, and charged particles trapped in local planetary magnetospheres, and undergo thermal cycling. The focus is on larger bodies of the outer Solar System such as the Jovian and Saturnian icy moons. Inorganic, organic and biological compounds may be present on/in surface ices. Such species could be delivered to icy surfaces through meteoric impacts or, on bodies such as Europa and Enceladus, potentially through active chemistry in subsurface liquid water. Research at JPL investigates the temperature-dependent chemical pathways available to mixtures of ices and inorganic/organic compounds subjected to energetic stimuli relevant to the outer Solar System.

This investigation includes a series laboratory experiments designed to elucidate the physical chemistry within ices relevant to icy solar system objects. The basic experimental approach is to engineer ice analogs constrained by model predictions and observations of solar system ices (composition, temperature, phase, structure, etc.). Once formed, the ices are systematically and quantitatively subjected to thermal cycling, UV photon irradiation, electron irradiation, etc. A number of analytical methods are applied to unravel the chemical and physical changes occurring in the samples. The investigation addresses questions such as: What are the essential chemical/physical properties of ices under conditions relevant to outer Solar System ices? What kind of chemistry can occur in these ices? This project is providing precise, accurate, and quantitative descriptions of the physical chemistry that occurs in outer Solar System ice analogs. This work provides a solid foundation for ground-truth understanding of observations obtained by JPL/NASA missions such as Galileo ISS, UVS, NIMS & Cassini ISS, VIMS and UVIS observations, and by ground-based facilities including Palomar Observatory, Table Mountain Observatory, NASA’s Infrared Telescope Facility, Arecibo, and Goldstone.

 

Radar Observations of Near-Earth Objects

Radar image of 1998 QE
A radar image of 1998 QE obtained by Deep Space Network’s Goldstone 70-meter tracking telescope. A binary companion is clearly visible in the image. The asteroid was about 6 million kilometers from Earth when this image was obtained.
  

Near-Earth Objects (NEOs) are asteroids or comets that approach or cross Earth’s orbit. They represent a potential hazard if they are both sufficiently large and on a path to impact Earth. JPL researchers have led efforts to discover and track NEOs, and are currently performing radar investigations of the properties of NEOs at radio telescopes in Arecibo, Puerto Rico, and at the Goldstone Deep Space Network in the Mojave Desert. These efforts are designed to understand the physical properties of NEOs such as their composition, roughness, size and gross structure, mechanical strength, dynamical properties, and surface texture. Many binary NEO systems have also been discovered with radar images. Complementary studies on the optical spectra and rotational states of NEOs are performed at Palomar Mountain and Table Mountain Observatory by JPL scientists. A better understanding of the nature of NEOs reveals their origins, collisional history, and the conditions under which they formed. Radar studies are also key for characterizing these bodies for further exploration by robotic spacecraft, including in situ samplers, and by astronauts.